1. Field of the Invention
The present invention generally relates to a pixel structure and the fabrication method thereof, and more particular, to a pixel structure for use in a liquid crystal display (LCD) and the fabrication method thereof.
2. Description of Related Art
Thin film transistor LCDs (TFT-LCDs) usually are classified into transmissive TFT-LCDs, reflective TFT-LCDs, and transflective TFT-LCDs, depending on the light source and the array substrate thereof. For the transmissive TFT-LCD, a backlight source is mostly used as the light source thereof, while the TFT array substrate uses transparent electrodes as the pixel electrodes so as to allow the light from the backlight source to pass therethrough. For the reflective TFT-LCD, a front-light source or an external light source is usually used as the light source thereof, while the TFT array substrate uses reflective electrodes made of a metal or of a material having good reflection characteristic as the pixel electrodes so as to reflect the light from the front-light source or the external light source. For the transflective TFT-LCD, which can be seen as a structure integration of a transmissive TFT-LCD and a reflective TFT-LCD, and a backlight source and a front-light source/external light source are simultaneously used for the display thereof.
FIGS. 1A-1D are diagrams showing the fabrication steps of a conventional pixel structure applicable to a transflective LCD. Referring to FIG. 1A, the fabrication of such conventional pixel structure includes the following steps. First, a substrate 110 is provided, and next, a gate 120, a gate insulation layer 130, a semiconductor layer 140, a source 150a and a drain 150b are sequentially formed over the substrate 110. The gate insulation layer 130 covers the gate 120. The semiconductor layer 140 is disposed on the gate insulation layer 130 and located above the gate 120, and the source 150a and the drain 150b are disposed on the semiconductor layer 140.
Referring to FIG. 1B, a passivation layer 160 is formed over the substrate 110 to cover the gate insulation layer 130, the source 150a and the drain 150b. In addition, the passivation layer 160 has a contact hole 160a to expose part of the drain 150b. Further, a plurality of bumps 170 is formed on part of the passivation layer 160. In more detail, a patterned photoresist layer (not shown) is formed on the passivation layer 160, followed by performing a reflow process on the patterned photoresist layer to complete forming the bumps 170.
Referring to FIGS. 1C and 1D, a reflective pixel electrode 180a and a transparent pixel electrode 180b are sequentially formed on the passivation layer 160, wherein the reflective pixel electrode 180a covers the bumps 170 and is electrically connected to the drain 150b through the contact hole 160a, while the transparent pixel electrode 180b covers the reflective pixel electrode 180a and is electrically connected to the drain 150b through the reflective pixel electrode 180a. 
Since the reflective pixel electrode 180a covers the bumps 170, the amount of the light reflected by reflective pixel electrode 180a is accordingly increased. However, since the bumps 170 are made of photoresist material containing a solvent, the reliability of the bumps 170 declines. Moreover, the total manufacturing cost is increased due to the cost of the bumps 170.